The invention relates to a supercharged gasoline internal combustion engine including a charger arranged in the engine intake air supply duct, which includes a throttle member upstream of the charger, and a secondary air duct branching off the intake air duct between the charger and the throttle member and leading to an exhaust duct of the internal combustion engine upstream of a catalytic converter. The secondary air duct includes a control valve, which can be controlled, together with the throttle member, by an electronic control unit to which engine operating parameters are supplied for controlling the throttle member and control valve.
The power output of an internal combustion engine is proportional to the airflow through the engine and the air density. Consequently, the engine power output can be increased by compression of the air before it enters the cylinders, that is, by a supercharger. The supercharger is arranged in the intake air duct for compressing the engine intake air. The air mass flow is controlled by the throttle member depending on the instant engine operating point. Before they are discharged to the environment, the exhaust gases of the internal combustion engine are conducted through a catalytic converter, wherein poisonous compounds contained in the exhaust gases are converted.
In order to heat the catalytic converter during the startup phase of the engine rapidly to the operating temperature needed for the conversion, part of the intake air is diverted and admixed to the exhaust gas as it is known from DE 44 41 164 A1. The oxygen added to the exhaust gas with the intake air causes in the catalytic converter an after-combustion, whereby the catalytic converter is heated. In this known arrangement, a secondary air conduct extends from an area of the intake air duct between the supercharger and the throttle to the exhaust duct upstream of the catalytic converter. The secondary air flow conduit is controlled by a flow control valve. The flow control valve and the throttle are connected, by control lines, to an electronic control unit. The control unit receives operating parameters of the internal combustion engine indicative of the engine operating state and the respective air mass flow (for example, the throttling cross-section of the throttle and the position of the control valve) from which it generates the control signals.
In addition to controlling the air mass flow the throttle also enhances the airflow through the secondary air pipe. During operation with secondary air flow when the control valve is open, the throttle may be adjusted beyond the point corresponding to the respective engine load, that is, the throttling cross-section may be reduced to such an extent that the back up pressure ahead of the throttle valve is increased and an increased amount of air is forced through the secondary air duct. Although part of the air is flowing through the secondary air duct, the charge air pressure can be maintained sufficiently high for the respective engine operating conditions by the closing of the throttle valve.
It is the object of this known arrangement to reduce costs and weight. It eliminates the need for air pumps and other components for supplying air to the catalytic converter to cause heating of the catalytic converter during the engine warm-up phase. However, the control arrangement requires an air circulation line by-passing the charger which is connected to the air supply duct downstream of the charger and which leads to the intake side of the charger. The air circulation line includes a control valve, which is controlled by the control unit. The control valve operating mechanism therefore includes an arrangement for a long-term adaptation and the control unit must include a complete performance graph for the angular position of the control valve depending on engine load and engine speed which is deposited in the control unit.
It is the object of the present invention to provide a control arrangement for a supercharged internal combustion engine, which permits air injection into the exhaust gas flow with little constructional expenses and which provides for optimal engine operating conditions.